Preparation And Properties Of Nickel Coated Graphite/Silicone Rubber Conductive Composites For Extrudate

Conductive rubber has excellent property of environmental sealing apart from high conductivity (volume resistivity ρv<0.1ohm-cm).On one hand, the cross section of many complicated shapes can be sealed by the rubber which has good flexibility and softness; on the other hand, conductivity can be imparted by the addition of conductive filler in the rubber matrix. The electromagnetic sealing material can be made by such conductive rubber in a wide range of wave frequency. Moreover, the molding methods are easily available and can produce many different complex shapes of products to meet the actual demand. This material is widely used in the electronic devices which need strict electromagnetic shielding effect.A new composite (SiR/NCG) with high conductivity was prepared. The nickel coated graphite (NCG) was dispersed in the silicone rubber (SiR) matrix. In this paper, the effect of the types and the amount of addition agents, the loading level of the conductive filler, processing method on curing characteristics as well as the conductive properties and mechanical properties of nickel coated graphite/silicone rubber composites were studied. Meanwhile, the optimal percolation threshold of the conductive filler was determined and the mechanism on the formation of electrically conductive network was discussed..At the same time, we also examined the influence of strain, stress and heat aging on the conductive stability.The effect of nickel coated graphite (NCG) loading level on the properties of the composites was researched. The results showed that the volume resistivity gradually declined and the percolation threshold was observed with the increase of the filler loading. The range of percolation threshold was180phr to250phr and the optimal filler loading was200phr. The effect of types and the amount of silane coupling agent, the amount of the curing agent on the properties of the composites were studied. The results showed that the curing time obviously increased and the curing rate decreased after the nickel coated graphite treated with silane coupling agent containing the double-bond. The conductive properties and mechanical properties were improved when the addition of vinyltriethoxysilane (A-151) was6phr.The relationship between conductive stability of the composites and the stress, strain and heat aging were examined. The results showed that the more the strain imposed, the more the conductive network was broken and the harder the network recovered. As the stress strain increasing, the breakup of conductive network was rising. When recovery time was longer, the network recovery became better. The volume resistivity declined as the heat aging time extended.The influence of mixing time, storage time and the curing time on the properties of the composites were studied. The results showed that as the mixing time became longer, the scorch time shortened and the degree of cure increased as well as the volume resistivity rose and the mechanical properties decreased. The volume resisitivity was great affected by the storage time, and the normal time was48h. When the curing temperature increased, the cross-linking agent was activated and the cross-linking bond of the composites broke up rapidly. The competition effect made the cross-linking degree raise at first, and then decline.